The transmission, routing and dissemination of information has occurred over computer networks for many years via standard electronic communication lines. These communication lines are effective, but place limits on the amount of information being transmitted and the speed of the transmission. With the advent of light-wave technology, a large amount of information is capable of being transmitted, routed and disseminated across great distances at a high transmission rate over fiber optic communication lines.
When information is transmitted over fiber optic communication lines, impairments to the pulse of light carrying the information can occur including pulse broadening (dispersion) and attenuation (energy loss). As an optical signal is transmitted over the fiber optic communication line, the optical signal is transmitted at various frequencies for each component of the optical signal. The high frequency components move through the fiber optic material at different speeds then compared to the low frequency components. Thus, the time between the faster components and the slower components increase as the optical signal is transmitted over the fiber optic communication line. When this occurs, the pulse broadens to the point where it interferes with the neighboring pulses; this is known as chromatic dispersion. Chromatic dispersion compensation corrects this pulse broadening.
Various chromatic dispersion compensation apparatus and methods are available.
In U.S. Pat. No. 6,259,845 entitled “Dispersion Compensating Element Having an Adjustable Dispersion” issued to Harshad P. Sardesai, a variable dispersion compensation module is disclosed. In the Sardesai patent, a dispersion compensation module including segments of optical fiber of varying lengths, some of which have a positive dispersion while others have a negative dispersion is disclosed. Selected optical fiber segments are coupled to one another to provide a desired net dispersion to offset the dispersion associated with the fiber optic communication line. The Sardesai patent allows for this variable dispersion compensation model rather than provide a unique segment of dispersion compensation fiber for each span. The Sardesai dispersion compensation module functions by interconnecting the various length of various dispersion per kilometer fibers so that the resulting total dispersion equals the dispersion of the fiber optic communication line span. The Sardesai dispersion compensation module, however, has a high cost in that multiple dispersion compensation fibers enclosed within the Sardesai compensation module may remain unused and are therefore wasted when implemented in the field. Further, the Sardesai dispersion compensation module requires excessive interconnectivity between the various dispersion compensation fibers, allowing for a greater connection loss to be experienced.
Published U.S. Patent Application No. U.S. 2001/0009468 entitled “Method and System for Compensating for Chromatic Dispersion in an Optical Network” by John Arthur Fee discloses a method and system which automatically adjusts the dispersion of an optical signal at any location in the optical network if the optical signal does not have a desired shape. In the Fee application, a method and system using a tunable dispersion compensator in an optical network is disclosed. The tunable dispersion compensators are provided throughout the optical network at amplifier locations or they may be provided at other locations within the network. The tunable dispersion compensator functions by fine tuning the shape of the optical signal until an optimal shape is obtained. The Fee application discloses an eye diagram analyzer which analyzes the optical signal and sends this information to the tunable dispersion compensator to allow for manipulation of the optical signal until the optimal “eye” shape is obtained. The eye is the area formed by the pulses of the optical signal.
Next, in published U.S. Patent Application U.S. 2001/0007605 entitled “Apparatus and Method of Compensating for Wavelength Dispersion of Optical Transmission Line” filed by Shinya Inagaki, et al., a tunable dispersion compensator is disclosed. In the Inagaki application, the dispersion compensation method uses dispersion compensation fiber in combination with the tunable dispersion compensation module to compensate for the chromatic dispersion. The tunable dispersion compensation module disclosed in the Inagaki application is a virtually imaged phased array (VIPA) type compensator. The chromatic dispersion is simultaneously compensated through the use of the dispersion compensation fiber and the VIPA type compensator.
U.S. Pat. No. 6,275,315 entitled “Apparatus for Compensating for Dispersion of Optical Fiber in an Optical Line” issued to Park, et al. discloses a dispersion compensation method in which dispersion compensation fiber is used in conjunction with a variable dispersion module. In the Park patent, the variable dispersion compensation module is a dispersion compensation filter such as a reflective etalon filter. The etalon filter is a tunable filter and thus allows for variable dispersion compensation.
The primary focus of the fiber optic industry to correct chromatic dispersion has followed one of two paths. The first path was for the use of variable dispersion compensation modules as has been disclosed in the above referenced patent/patent applications. A second path is to manufacture dispersion compensation fibers in varying lengths to correct for dispersion compensation. Each varying length of the dispersion compensation fiber must be inventoried requiring a vast amount of assets to be tied up in inventory which is infrequently implemented. Therefore, any advancement in the ability to reduce the number of interconnectivity points between the dispersion compensating fibers and to reduce the cost incurred with the highly technical variable dispersion compensators and the high cost of inventory would be greatly appreciated.